1. Field of the Invention
The present invention relates to a thin film magnetic head for writing and a method of manufacturing the same, and more particularly relates to a combination type thin film magnetic head including an inductive type thin film magnetic head for writing and a magnetoresistive type magnetic head for reading, said magnetic heads being supported by a substrate in a stacked fashion.
2. Description of the Related Art
Recently a surface recording density of a hard disc device has been improved, and it has been required to develop a thin film magnetic head having an improved performance accordingly.
There has been proposed and actually used a combination type thin film magnetic head including an inductive type thin film magnetic head for writing and a magnetoresistive type magnetic head for reading, said magnetic heads being supported by a substrate in a stacked fashion. As the reading magnetic head utilizing the magnetoresistive effect, there has been generally used a reading magnetic head utilizing an anisotropic magnetoresistive (AMR) effect, but there has been also developed a magnetic head utilizing a giant magnetoresistive (GMR) effect having a resistance change ratio higher than the normal anisotropic magnetoresistive effect by several times.
In the present specification, these AMR and GMR elements are termed as a magnetoresistive type thin film magnetic head or simply MR reproducing element.
By using the AMR reproducing element, a very high surface recording density of several gigabits per a unit square inch has been realized, and a surface recording density can be further increased by using the GMR element. By increasing a surface recording density in this manner, it is possible to realize a hard disc device which has a very large storage capacity of more than 10 gigabytes and is still small in size.
A height (MR Height: MRH) of a magnetoresistive reproducing element is one of factors which determine a performance of a reproducing head including a magnetoresistive reproducing element. This MR height MRH is a distance measured from an air bearing surface on which one edge of the magnetoresistive reproducing element is exposed to the other edge of the element remote from the air bearing surface. During a manufacturing process of the magnetic head, a desired MR height MRH is obtained by controlling an amount of polishing the air bearing surface.
At the same time, a performance of a recording head has been also required to be improved. In order to increase a surface recording density, it is necessary to make a track density on a magnetic record medium as high as possible. For this purpose, a width of a pole portion at the air bearing surface has to be reduced to a value within a range from several micron meters to several submicron meters. In order to satisfy such a requirement, the semiconductor manufacturing process has been adopted for manufacturing the thin film magnetic head.
One of factors determining a performance of an inductive type thin film magnetic film for writing is a throat height (TH). This throat height TH is a distance of a pole portion measured from the air bearing surface to an edge of an insulating layer which serves to separate electrically a thin film coil from the air bearing surface. It has been required to shorten this distance as small as possible. Also this throat height TH is determined by an amount of polishing the air bearing surface.
In order to improve the performance of the combination type thin film magnetic head including a stack of an inductive type thin film magnetic head for writing and a magnetoresistive type thin film magnetic head for reading, it is important that the inductive type thin film magnetic head for writing and magnetoresistive type thin film magnetic head for reading are formed with a good balance.
FIGS. 1-11 show successive steps of manufacturing a known typical thin film magnetic head, in which A represents a cross sectional view cut along a plane perpendicular to the air bearing surface and B denotes a cross sectional view cut along a plane parallel with the air bearing surface. FIGS. 12-14 are a cross sectional view illustrating a completed thin film magnetic head, a cross sectional view of the pole portion, and a plan view depicting the whole magnetic head. This magnetic head belongs to a combination type thin film magnetic head which is constructed by stacking an inductive type thin film writing magnetic head and a magnetoresistive type thin film reading magnetic head one on the other.
At first, as illustrated in FIG. 1, on a substrate 1 made of, for instance aluminum-titan-carbon (AlTiC), is deposited an insulating layer 2 made of alumina (Al.sub.2 O.sub.3) and having a thickness of about 5-10 .mu.m.
Then, as depicted in FIG. 2, a first magnetic layer 3 constituting one of magnetic shields for protecting the MR reproducing magnetic head from external magnetic fields is formed to have a thickness of 3 .mu.m on the insulating layer.
Then, after depositing by sputtering a shield gap layer 5 made of an alumina with a thickness of 100-150 nm as shown in FIG. 3, a magnetoresistive layer 4 having a thickness of several tens nano meters and being made of a material having the magnetoresistive effect, and the magnetoresistive layer is shaped into a desired pattern by a highly precise mask alignment.
Next, as represented in FIG. 4, a second magnetic layer 6 made of a permalloy and having a thickness of 3 .mu.m is formed. This magnetic layer 6 serves not only as an upper shield layer for magnetically shielding the MR reproducing element together with the above mentioned bottom shield layer 3, but also as a bottom magnetic layer of the inductive type writing thin film magnetic head to be manufactured later.
Next, after forming, on the second magnetic layer 6, a write gap layer 7 made of a nonmagnetic material such as alumina to have a thickness of about 200 nm and a given pattern, a seed layer 8 made of a magnetic material is formed with a thickness of 50-80 nm and a photoresist 9 is formed thereon in accordance with a given pattern as illustrated in FIG. 4.
Then, an electroplating is performed by using the seed layer 8 as one of electrodes and the photoresist 9 as a mask to deposit selectively a magnetic material having a high saturation magnetic flux density such as a permalloy and iron nitride to form a pole chip 10 as well as a connecting magnetic layer 11 for connecting the second magnetic layer 6 with a third magnetic layer constituting the other pole.
Then, after removing exposed portions of the seed layer 8 by etching, in order to prevent an increase of an effective track width, that is, in order to prevent a spread of a magnetic flux at the lower pole during a writing operation, the gap layer 7 and second magnetic layer constituting the pole portion near the pole chip are removed by an ion beam etching such as an ion milling to form a trim structure. Furthermore, an insulating layer 12 made of alumina is formed to have a thickness of about 3 .mu.m, and then an assembly is flattened by, for instance chemical-mechanical polishing (CMP).
After that, as depicted in FIG. 7, after forming an electrically insulating photoresist layer 11 is formed in accordance with a given pattern by a highly precise mask alignment, a seed layer 14 made of copper is formed on the photoresist layer 11, and then a photoresist layer 15 is formed on the seed layer.
Then, the electroplating is performed by using the seed layer 14 as one of electrodes and the photoresist layer 15 as a mask to deposit copper with a thickness of 2-3 .mu.m to form a first layer thin film coil 16 as depicted in FIG. 8. It should be noted that the thin film coil is formed by the seed layer and copper layer deposited thereon by the electroplating, but for the sake of explanation, the copper layer deposited by the electroplating is referred to as the thin film coil.
Next, as depicted in FIG. 9, an insulating photoresist layer 17 is formed such that the thin film coil 16 is supported in an insulated and isolated manner, a surface of the photoresist layer is flattened by baking at a temperature of, for instance 250-300.degree. C. During this baking, a periphery of the lower insulating layer 13 is also round. Furthermore, in order to form a second layer thin film coil, a seed layer 18 made of copper is formed with a thickness of 50-80 nm on the pole chip 10 and photoresist 17.
Furthermore, after forming a photoresist serving as a mask on the seed layer 18 in accordance with a given pattern, the electroplating is carried out by using the seed layer as one of electrodes and the photoresist as the mask to deposit copper selectively on the seed layer to form a second layer thin film coil 19. After removing the photoresist and exposed portions of the seed layer 18, a photoresist 20 is formed such that the second layer thin film coil is supported thereby in an insulated and isolated manner, and then the sintering is performed at about 250.degree. C. to obtain a flat surface as shown in FIG. 10.
Next as illustrated in FIG. 11, on the pole chip 10 and photoresist layers 13, 17 and 20, a yoke portion 21 constituting the other pole is selectively formed with a thickness of 3 .mu.m in accordance with a given pattern.
This yoke portion 21 is brought into contact with the second magnetic layer 6 at a rear position remote from the pole portion by means of the connecting magnetic layer 11, and therefore the thin film coils 15, 19 pass through a closed magnetic path constituted by the second magnetic layer, pole chip and yoke portion.
Furthermore, an overcoat layer 22 made of an alumina is deposited with a thickness of 20-30 .mu.m on an exposed surface of the yoke portion 21 as well on surfaces of other parts.
Finally, as shown in FIG. 12, a side wall at which the magnetoresistive layer 4, write gap layer 7 and pole chip 10 are formed is polished to form an air bearing surface (ABS) 23 which is opposed to a magnetic record medium. It should be noted that in FIG. 12, the overcoat layer 22 is dispensed with.
During the formation of the air bearing surface 23, the magnetoresistive layer 4 is also polished to obtain an MR reproducing element 24. In this manner, the above mentioned throat height TH and MR height MRH are determined by the polishing. In an actual manufacturing process, contact pads for establishing electrical connections to the thin film coils 15, 19 and MR reproducing element 24 are formed, but these contact pads are not shown in the drawings. FIG. 13 is a cross sectional view of the pole portion of the combination type thin film magnetic head thus manufactured, while the pole portion is cut along a plane parallel with the air bearing surface 23.
As shown in FIG. 12, an angle .theta. between a straight line S connecting side edges of the photoresist layers 13, 17, 20 isolating the thin film coils 15, 19 and an upper surface of the yoke portion 21 is called an apex angle. This apex angle is one of important factors for determining a property of the thin film magnetic head together with the throat height TH and MR height MRH.
Furthermore, as shown in the plan view of FIG. 14, a width W of the pole chip 10 determines a width of tracks recorded on a record medium, and therefore it is necessary to make this width W as small as possible in order to realize a high surface recording density. Recently, this width has been required in the order to sub-microns. The yoke portion 21 also has a narrow pole portion which is coupled with the pole chip 10, but its width is somewhat larger than the width of the pole chip 10. It should be noted that in the drawing, the thin film coils 15, 19 are denoted to be concentric for the sake of simplicity.
In the known method of manufacturing the thin film magnetic head, there is a special problem in the formation of the top pole after the formation of the thin film coil in a precise manner along the outwardly protruded coil portion, particularly along an inclined portion (Apex) thereof, said coil portion being covered with the photoresist insulating layers.
That is to say, in the known method, upon forming the top pole, after a magnetic material such as permalloy is deposited by plating on the outwardly protruded coil portion having a height of about 7-10 .mu.m, a photoresist is applied to have a thickness of 3-4 .mu.m, and then the photoresist layer is shaped into a given pattern by utilizing the photolithography.
Since a thickness of the photoresist layer provided on the upper portion of the coil portion should be at least 3 .mu.m, the photoresist layer has to be applied such that a portion of the photoresist at a bottom of the outwardly protruded coil portion would have a thickness of about 8-10 .mu.m.
On the other hand, in order to form a narrow track of the recording head near the edges of the photoresist insulating layers (for instance, layers 11 and 13 in FIG. 7), the top pole should be patterned to have a width of about 1 .mu.m. Therefore, it is necessary to form a pattern having a width of 1 .mu.m in the photoresist layer having a thickness of 8-10 .mu.m.
However, when such a narrow pattern having a width of 1 .mu.m is to be formed with the thick photoresist layer having a thickness of 8-10 .mu.m, a top pole which can realize a narrow track could hardly be manufactured accurately due to a deformation of a pattern by light reflection during a light exposure in a photolithography and an inevitable decrease in a resolution caused by a large thickness of the photoresist layer.
In order to mitigate such a problem, as shown in FIGS. 1-14, the top pole is divided into the pole chip 10 and the yoke portion 21 connected therewith, and a width of the pole chip is narrowed to decrease a width of the record track width.
However, the thin film magnetic head, particularly the recording magnetic head formed in the above mentioned manner still has the following problems.
If there is an alignment error in the photolithography for forming the yoke portion 21 on the pole chip 10 having the narrow width W, a center of the pole chip 10 and a center of the pole portion of the yoke portion 20 viewed from the air bearing surface might be shifted relative to each other. If the center of the pole chip 10 is deviated from the center of the pole portion of the yoke portion 20, there might be produced a large leakage of the magnetic flux from the pole portion of the third magnetic layer and data might be written by this leaked magnetic flux. Therefore, an effective track width is increased and data might be recorded in a region other than a desired region into which the data has to be recorded.
In the known thin film magnetic head, the edge of the pole chip 10 opposite to the air bearing surface 23 is used as a reference position of throat height zero. However, since the pole chip has a small width W, the edge of the pole chip is rounded off and therefore a position of the edge of the pole chip might be shifted. In the conventional combination type thin film magnetic head, although the throat height TH and MR height MRH have to be set accurately with reference to the throat height zero position, since the reference position of throat height zero might deviate during the manufacturing process and could not be defined accurately, the thin film magnetic head having desired throat height TH and MR height MRH according to the desired design values could not be manufacture with a high yield.
Moreover, in the known method of manufacturing the thin film magnetic head, the seed layer 8 serving as one of the electrodes for the electroplating for forming the pole chip 10 and the seed layer 14 serving one of the electrodes for the electroplating for forming the first layer thin film coil 15 (2) are formed separately from each other and the steps for removing these seed layers are performed separately. Therefore, the number of manufacturing steps is large, the through put is decreased, and the manufacturing cost is increased.